1. Field of the Invention
The present invention relates to an apparatus and method of assay in utilizing attenuated total reflection. More particularly, the present invention relates to an apparatus and method of assay in utilizing attenuated total reflection, in which a sensor unit for assay can be positioned reliably to prevent leakage of fluid in use of pipette devices.
2. Description of the Related Art
An assay apparatus for assay in utilizing attenuated total reflection is used for various kinds of studies in a biochemical field or the like, for example to study interaction of protein, DNA and various biomaterials, and to select candidate drugs by screening.
A surface plasmon resonance (SPR) sensor is known as an assay apparatus in utilizing attenuated total reflection. Surface plasmon is a term to mean the compressional wave created on the surface of the metal and included in plasmon as quantized expression of the compressional wave. Free electrons in a metal vibrate to generate the compressional wave.
U.S. Pat. Nos. 5,164,589 and 5,313,264 (corresponding to JP-B 3294605) disclose an SPR assay apparatus in which an optical system of Kretschmann configuration is used for incidence of light to the metal film. According to the Kretschmann configuration, the thin film/dielectric interface of the metal film is fitted on a prism, which condenses light and directs the light to the thin film/dielectric interface in a manner conditioned for total reflection. A sensing surface is overlaid inside the flow channel, for immobilizing the sample. Reaction of the sample is caused on the sensing surface. Illuminating light is applied to the interface of the metal film through the prism to satisfy the total reflection condition, to measure reflected illuminating light.
Upon the total reflection created on the metal/dielectric interface, a small component of the light passes through the metal film without reflection, and penetrates to the sensing surface. A wave of the penetrating component is called an evanescent wave. Surface plasmon resonance (SPR) is created when frequency of the evanescent wave coincides with that of the surface plasmon. In response to this, intensity of the reflected light attenuates remarkably. In the assay apparatus, the attenuation in the reflected light reflected by the metal/dielectric interface is detected, to recognize creation of the SPR on the sensing surface.
A sample or biomaterial, such as protein and DNA, is handled as sample fluid for the purpose of preventing deactivation or modification due to drying. Examples of its content of fluids include pure water, physiological saline water, liquid buffer and the like. The assay apparatus of U.S. Pat. Nos. 5,164,589 and 5,313,264 (corresponding to JP-B 3294605) assays the interaction of the samples. A flow channel is formed at the sensing surface for flow of the sample fluid. The flow channel and the prism are disposed on the assay stage disposed on the apparatus body. A sensor unit of the chip type having the metal film on the support of glass is loaded in the assay stage for assay.
U.S. Pat. Nos. 5,164,589 and 5,313,264 (corresponding to JP-B 3294605) discloses a connector block secured to the flow cell for connecting a tube with the flow channel. However, contamination is likely to occur in the structure with the tube, because a first fluid may be stuck on the inside of the tube and a second fluid will enter and mixes with the residue of the first fluid.
To solve such a problem, it is conceived with an SPR assay apparatus to use a pipette device having a pipette head and a pipette tip fitted on an end of the pipette head in a removable manner. A fluid such as a sample fluid stored in a reservoir is dispensed and introduced to a flow channel inside the assay apparatus. The pipette tip is exchanged at each time the fluid in use is changed over, so contamination of the fluid is prevented in the flow of the fluid to the flow channel.
A sensor unit is used with the assay apparatus, and includes a flow cell, a prism, and a sealing mechanism. The flow cell has the flow channel. A metal film or thin film is overlaid on the prism. The sealing mechanism keeps a lower face of the flow cell fitted on the upper face of the prism, for positioning the metal film in the flow channel. The flow channel is a conduit formed in a U-shape in the flow cell. Ends of the flow channel are open in the upper surface of the flow cell. A lower side of the flow channel is open, and is closed by the metal film. When the fluid is introduced to the flow channel, the fluid contact the metal film positioned in the flow channel. When the fluid is introduced by the pipette device to the flow channel, an end of the pipette device is set at one of the ends of the flow channel, to dispense and introduce the fluid.
However, a problem is likely to arise in incidental offsetting of the sensor unit upon inserting the pipette device in the flow channel or removing the pipette device from the flow channel. As a detection signal of the SPR is very fine, small offsetting of the sensor unit will cause an error in the assay. Also, a direction of removing the pipette device from the flow channel is reverse to a direction of the sealing mechanism pressing the flow cell on the prism. Force of pressing the flow cell will decreased in removal of the pipette device. A gap may occur between the flow cell and the prism, to leak the fluid from the flow channel.